TwlNmenu is the name for an application that comes bundled with Nintendo DSi SDK's, also known as Panda DSi's by the community. This application would install *.TAD files, an installable archive developed by Nintendo, similar to RocketRobz's cancelled *.TIA file format.

TwlNmenu's icon.

First surface

The existance of NandFiler and TwlNmenu was discovered at Gamescom 2009 when users by the name of Demo and Shadowchao started discussions about 2 development apps. Unfortunatly, both were unable to open the applications, because there was security walking around and the Nintendo DSi unit was hooked up to a monitor. Fast-forwarding to Febuary 11th, 2013, a collector by the name of LimboFunk mentioned a Nintendo DSi Development Unit, as well as the correct names for the applications. There wasn't much discussion after that, except for references, with no dumps being made. However, on September 2nd, 2017, a TWLSDK was leaked containing WMTestTool, RelayStation, modified versions of DS Download Play and Rev. 11364 of NandFiler and TwlNMenu.

Screenshots

 
Icon of TwlNmenu showing the contents of a SD Card.
 
When a *.TAD file has been selected, it will ask if you want to install it.
 
Highlighting the NAND. It shows all the applications installed in folder 00030004.